The asymmetric unit of the title compound, 2C(5)H(7)N(2) (+)·SO(4) (2-)·H(2)O, contains two 4-amino-pyridinium cations (A and B), a sulfate dianion and a water mol-ecule. One of the 4-amino-pyridinium cations (B) is disordered over two orientations with refined site occupancies of 0.568 (4) and 0.432 (4). The non-H atoms of the 4-amino-pyridinium cations are essentially coplanar, with a maximum deviation of 0.055 (1) Å (in cation A), 0.022 (3) Å (for the major component in cation B) and 0.009 (3) Å (for the minor component in cation B). In the crystal, the sulfate O atoms link the 4-amino-pyridinium cations and water mol-ecules into a three-dimensional network via inter-molecular O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds. The crystal structure is further consolidated by N-H⋯O(water) and C-H⋯O(water) hydrogen bonds.